Scientific Forecaster Discussion
fxus65 kcys 220604
Area forecast discussion
National Weather Service Cheyenne Wyoming
1204 am MDT sun Sep 22 2019
issued at 636 PM MDT Sat Sep 21 2019
Sent update to issue freeze warnings for the Upper North Platte
River basin, including Saratoga, and southwestern Carbon County.
High clouds are either pushing to the east or will over the next
several hours. With pretty light winds, clearing skies, and low
dewpoints, expect these areas to drop below freezing tonight.
Further east, cloud cover will struggle to push east of the
Laramie valley as an upper level trough axis takes it time to
eject. The Laramie valley should get pretty cool tonight, so
decided to issue a frost advisory for that area starting at 300
Short term...(this evening & overnight)
issued at 241 PM MDT Sat Sep 21 2019
We have two main near-term concerns during the evening & overnight
hours across the region. A freeze watch is in effect for mountains
and high valleys across southern Carbon & Albany counties for late
tonight and early Sunday. A rather potent mid-level disturbance is
progged to sweep across the region tonight, bringing the potential
for considerable mid/high level cloud cover which could impact our
low temperature readings. It should still get quite cold with lows
in the mid 30s, but confidence in a hard freeze is not high enough
to warrant an upgrade to a warning at this time. Further east, the
potential for showers & thunderstorms will likely increase tonight
for our southeastern zones, roughly along/southeast of a line from
Cheyenne to Alliance. The air mass across the region remains quite
dry. However, moisture advection is already being evidenced by the
robust increase in cloud cover upstream over Colorado. Models show
excellent low-level frontogenesis and thermal advection over these
areas, and the hrrr has remained very consistent W/a strong signal
for a heavier SW-NE oriented precipitation band between 3-9z. This
seems to make sense with locally induced cyclogenesis taking place
in the Chugwater area later this evening. It would not be all that
surprising to see some sort of mesoscale convective vortex take shape, so we opted to bump
up pops into the likely category. Thunderstorms will gradually end
Long term...(sunday - saturday)
issued at 342 am MDT Sat Sep 21 2019
Warming trend expected to commence Sunday afternoon through Tuesday
accompanied with dry conditions. Another cold front appears possible
mid-week but overall precipitation chances appear low at this
time as temperatures return back to normal values.
With the departing trough by Sunday to be quickly followed by a
shortwave ridge pattern, warm air advection will commence quickly after the cold
Sunday morning start. A return to dry, west winds will allow for
fire danger to increase, especially on Monday. Warmth continues in
Tuesday with values 4-7f degrees above normal. A broad longwave
trough should shift across the northern Continental U.S. Mid-week per multi-
model ensemble guidance and bring a cold front through the region.
However, given the low amplitude and limited moisture, overall
rain chances appear low at this time. After a quick cool down
Wednesday, a quick warm up may occur late week depending on
overall pattern evolution of a once cut-off low ejecting northeast
and bringing warm air advection in the southwest flow. For late week into next
weekend, southeast Wyoming and west NE may be just too far east of a large
trough along the entire West Coast for possible sensible weather
impacts. Stay tuned on the development of this trough as it
evolves over the next week.
Aviation...(for the 06z tafs through 06z Sunday night)
issued at 1137 PM MDT Sat Sep 21 2019
Showers will continue across the southwest portion of the Nebraska
Panhandle through 22/09z, primarily effecting kaia and ksyn.
Another round of showers will effect east central Wyoming and the
northwest portion of the Panhandle beginning from west to east at
22/08z across Converse County and pushing east of kcdr at 22/16z.
VFR conditions expected for the period, with a low to mid VFR
ceilings at first, clearing out after 22/15z as dry westerly
winds pick up with gusts to 25 kts at all terminals. Winds will
diminish around 23/00z. Fog possible at ksyn between 22/09-15z if
the winds drop sufficiently.
issued at 241 PM MDT Sat Sep 21 2019
Lower fire weather risks today with cooler temperatures and slightly
greater moisture in place. However, winds will remain elevated across
the high terrain at 30 to 40 mph through the afternoon. Lower humidity
values will return Sunday through Tuesday as temperatures slowly warm.
Elevated to near-critical fire weather conditions return during this
period and can not fully rule out localized red flag conditions early
next week across southeast Wyoming, especially Monday afternoon.
Wyoming...freeze warning until 9 am MDT Sunday for wyz111-113.
Frost advisory from 3 am to 9 am MDT Sunday for wyz115.